1. Field of the Invention
The present invention relates to a concave diffraction grating device and a reflective dispersion device for spectral measurement, as well as a spectral device incorporated with the concave diffraction grating device or the reflective dispersion device.
2. Description of the Related Art
Conventionally, there is known a technique of integrally forming an optical element such as a lens or a mirror, and a diffraction grating to product a compact spectral device. A diffraction grating device integrally formed with a diffraction grating and a concave mirror is disclosed in e.g. Japanese Unexamined Patent Publication No. Hei 8-271335 (D1) or Japanese Unexamined Patent Publication No. 2006-98428 (D2). The diffraction grating device disclosed in D1 is produced by a holographic exposure method, wherein a concave mirror having a curvature of a first plane parallel to a grating groove of a diffraction grating and a curvature of a second plane orthogonal to the first plane different from each other is subjected to holographic exposure. The diffraction grating device disclosed in D2 is produced by a replica method using a master diffraction grating created by the holographic exposure method to realize mass-production.
The technology disclosed in D1 has the following drawback. Even if aberration at a design central wavelength with respect to oblique incidence is corrected by directly forming an incident slit image on an exit slit, with use of a diffraction grating produced by recording an unequal-interval, non-linear grating pattern by the holographic exposure method, aberration particularly, astigmatism at the other wavelength may remain. Also, in view of the point that the diffraction grating is a nonlinear diffraction grating, it is difficult to form a replica of the nonlinear diffraction grating, thereby making it difficult to produce replicas. In the technology disclosed in D2, it is difficult to reproduce the design and the configuration of a master diffraction grating in details, in view of the point that transferring is performed substantially two times in the replica method.